cereal

nouns

grass whose starchy grains are used as food: wheat; rice; rye; oats; maize; buckwheat; millet
foodstuff prepared from the starchy grains of cereal grasses
a breakfast food prepared from grain
is a type of (narrower)
any food (especially cereal) usually served for breakfast

adjectives

made of grain or relating to grain or the plants that produce it
"a cereal beverage"; "cereal grasses"
pertains to